The present application relates to a liquid crystal drive device for driving a liquid crystal display device and more particularly, to a liquid crystal drive device capable of achieving reduction in power consumption.
A liquid crystal display device comprises a liquid crystal display panel, and a liquid crystal drive device supplying various signals and voltages for effecting display on the liquid crystal display panel. The liquid crystal display device currently in the mainstream of a display device for various types of electronic equipment is the so-called active-matrix type having active elements in a pixel circuit. Since thin-film transistors are generally used as the active elements, and the active elements are described as the thin-film transistors in the present specification.
This type of liquid crystal display device comprises a liquid crystal display panel having a plurality of source electrode interconnects extending in a first direction (for example, a longitudinal direction) on an inner face of an insulating substrate and juxtaposed in a second direction (for example, a transverse direction) intersecting the first direction, a plurality of gate electrode interconnects extending in the second direction and juxtaposed in the first direction, a thin-film transistor disposed at respective crossover points of the source electrode interconnects and the gate electrode interconnects, constituting a pixel respectively, a plurality of common electrode interconnects for applying a common electrode voltage (hereinafter referred to merely as “common voltage” as well) to common electrodes disposed through the intermediary of a liquid crystal layer, respectively, and an external terminal coupled in common to the common electrode interconnects, and a liquid crystal drive circuit supplying various signals and voltages for effecting display on the liquid crystal display panel. In this connection, the liquid crystal display device is not limited to one wherein the plurality of common electrode interconnects are coupled in common to the external terminal (also referred to as a common electrode terminal, or merely as a common electrode), outside a pixel region (display region) of the liquid crystal display panel but some liquid crystal display panel has common electrodes serving as a flat electrode in common to all pixels.
In display operation of the liquid crystal display device, the thin-film transistor of the pixel selected by a select voltage applied to one of the gate electrode interconnects is turned on, and an alignment direction of the liquid crystal layer interposed between a pixel electrode and the common electrode, coupled to the thin-film transistor, is caused to change, thereby controlling a quantity of transmitted light or reflected light. The common voltage applied to the common electrode at this point in time is generated by use of a voltage boosted by a boost circuit. The above and other objects and novel features of the invention will more fully appear from the following detailed description when the same is read in conjunction with the accompanying drawings. Specific examples of a conventional liquid crystal display device and a conventional liquid crystal drive device for driving the same, respectively, are described later in contrast with the present invention under the item “DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS”.